Rate of flow differential pressure combining device



May 9, 195%) F. J. WIEGAN ET AL.

RATE OF FLOW DIFFERENTIAL PRESSURE COMBINING DEVICE Filed Dec. 7, 194.5

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Patented May 9, 1950 FFICE RATE OF FLOW DIFFERENTIAL PRESSURE COMBINING DEVICE Francis J. Wiegand, Ridgewood, and Mark E. Rowe, West Englewood, N. J., assignors to Wright Aeronautical Corporation, a corporation of New York Application December '7, 1945, Serial No. 633,562

7 Claims.

This invention relates to flow measuring means and is particularly directed to means for measuring flow in a duct in which there is likelihood of a non-uniform distribution of flow across the duct.

Venturi measuring system for measuring the air flow through the intake duct of an internal combustion engine have comprised a pair of spaced Venturi tubes disposed in said duct. The two Venturi throat pressures are transmitted to a common passage and the pressure difierence between the resultant of the throat pressures and the average impact pressure has been used as a measure of the air flow through the duct. However, assuming that theaverage velocity across the duct is approximately equal to the arithmetic average of the fluid velocities at the entrance to each Venturi tube, then the aforementioned pressure difference is not an accurate measure of the average fiow through the duct. This is so since the flow through a Venturi tube is not proportional to the Venturi pressure differential and, instead, is proportional to the square root of the Venturi pressure differential. As a result, if the resultant pressure difierential of the two Venturi tubes is to be an approximate measure of the average air flow, this pressure differential should be approximately proportional to the square of the arithmetic average of the square roots of the individual pressure difierentials of each Venturi tube. Actually, however, when the throat pressures of the two Venturi tubes are transmitted to a common passage, the resulting pressure differential is approximately equal to the arithmetic average of the two Venturi pressure differentials and, in general, this resulting pressure difierential is greater than the aforementioned desired pressure differential.

Accordingly, it is an object of this invention to provide means for combining the pressure differentials obtained from two Venturi tubes in a common fluid flow duct such that the square root of the resulting pressure differential is proportional to the average flow through the duct. Specifically, the invention comprises a valve which is arran ed to throttle the larger of the two Venturi suction pressures. In this way, the resultant pressure diilerential obtained, from the combination of the two Venturi pressure differentials can be made to closely approximate the proper value for the average flow through the duct.

'- Other objects of this invention will become apparent upon reading the annexed detailed description in connection with the drawing in which:

Figure 1 is a diagrammatic sectional view illustrating one embodiment of the invention; and

Figure 2 is a sectional view of a modified form of a portion of Figure 1.

Referring to Figure 1, l0 designates an air intake duct for an internal combustion engine across which the air flow tends to be non-uniformfor example, because of the bend illustrated in this duct. A section I2 of the duct is provided with a pair of sideby-side main Venturi tubes Ed and it through which passes all the air flowing through the duct. The main Venturi tube M is provided with a boost Venturi tube I8 and the main Venturi tube It is provided with a boost Venturi tube 2%. The boost Venturi tubes l8 and 2% are supported from the duct section l2 by the arms 2% and 22 respectively. Passages 2t and 2% within the arms 20 and 22 open into the throats of the Venturi tubes is and 2!! respectively and communicate with a common passage 28.

The impact pressure of the air entering the main and boost Venturi tubes is transmitted through tubes to the annuli 32 and 34 provided by the main Venturi tulbes i4 and [6 respectively. These annuli are connected together by the passage 35 and the pressure therein is transmitted to a passage 38. The passages 28 and 38 are in communication with chambers 40 and G2 on opposite sides of a diaphragm M supported by and extending across a housing 46. In this way, the diaphragm M is subjected to a pressure difference which is a function of the magnitude of the air flow through the duct Hi.

The housing is is also provided with fixed partitions 63 and as and a flexible diaphragm 54 extending thereacross. The flexible diaphragms 44 and 55 are connected together for joint movement by a valve stem 55. The valve stem extends through an opening 55 in the fixed partition and has a valve head 60. A small flexible diaphragm 52 provides a seal between the valve stem 5% and the fixed partition 58 and small flexible diaphragms ed and 5% provide seals at the ends of the valve stem. Fuel under pressure is supplied from a conduit 6% to a chamber 10 from which it flows through the valve opening 58 into a chamber 12. From the chamber 12, the fuel flows through a restricted orifice M in the conduit It from which it discharges into the air duct it; below the throttle valves 18. The fuel pressure downstream oi the orifice 14 is transmitted to a chamber 16 whereby the flexible diaphragm 54 is subjected to a fuel pressure differential substantially proportional to the fuel flow. The remote sides of the small flexible diaphragms 64 and 66 are placed in communication with each other and to a suitable source of pressure through a passage 89. With this construction, the diaphragms 44 and 54 position the fuel valve 60 so that the air pressure difierential across the diaphragm 44 balances the fuel pres; sure differential across the diaphragm 54. In this way, the magnitude of the fuel flow to, the internal combustion engine is controlledby the magnitude of the air flow. The sttucture sa far}- described is quite conventional and the particu-. lar manner in which the air flow pressure di-f ferential controls the fuel flow forms no part of the present invention. It also v conpnon prac; tice to provide a restricted bleed passage 82 around the diaphragm 44.

With the present invention, the air pressure in the cham er 42 is automatica l o r d a spherical member 84 supported by a flexible diaphragm 8.6. diaphragm 86 extends across a housing to, provide a pair of chambers 88 and 8!! into. which open the passages 24 and 25 respectively. The member 84 is movable with the diaphragm 8.5; to control the air fiow from the chambers. 8.8. and 99 into the passages 24' 25. Accordingly the member 84 comprises a flow restrictorwhich upon movementv toward the. passage 2.4 restricts the flow through said passage from the chamber 38 relative to the flow through passa e 26 from the chamber 99, while move.- ment of said; member 86, toward the passage 2'5 restricts the flow through the passage 26 relative to. that through the passage 24. In addition, the chambers 88 and Sil are incommunication with the passage 28 through restricted openings 92 and 9.4. respectively.

With this construction, during engine operaticn, there is a continual of airfrom the impact tubes passage 38, chamber 46, restricted bleed passage 82, chamber to the passage From thepassage 28 this airflow div des through the. two restrictions 92 and into chambers 83 and 99 and thence into passages. 2 and 265-110 the throatsof the two Venturi tubes 8 and 20 respectively. Assuming that the restrictions 92- and 94 are the same then if there is any difference in the Venturi. throat pressures-401 example, if the throat pressure of the Venturi tubes 18 is less than the throat pressure of the Venturi tube 29-. there will be a larger air flow through the restriction 92 into the chamber 38; to, the Venturi tube [8 than the air fiow through the restriction into the chamber cc to the Venturi tube Ihis result. follows. from a. smaller pressure the chamber 38 than in the. chamber 98 so that the diaphragm 85 will move the member 84 to the left. to throttle the air flowing from the chamber 8.8. to. the Venturi tube i8 until the pressures balance on the two sides of the diaphragm 85.

In this way, the valve 84 automatically decreases the air pressure differential across the diaphragm M from what it would be in the ab-- sence of the member as and the extent. to which the pressure. differential is decreased depends on the extent to which the. air flow through the Venturi tubes ifland Ellis unequal.

If desired, the relative. efiect of the pressure difierences of the two Venturi tubes on the pressure differential across the diaphragm M may be modified by providing small by-pass passages 9 6 and 98 respectively around the ends of the passages 24 and 26 controlled by. the member 84. Said by-pass passages may be made adjustable. In addition, the pressure differential across the diaphragm 44 may be changed by varying the relative size of the restrictions 92 and 94. Also, spring means may be provided to urge the valve 84 toward the passage 26 or 26. These features may be used singly or in combination and in this way the pressure difierential across the diaphragm 44 can be made to be an accurate measure of the average air flow through the dil Figure 2 illustrates a modification in which. the. aforementioned springs have been added to the valve. In this modification, a needle type valve. HQ has been illustrated instead of the spherical member 84 of Figure 1. However, the particular shape oi the member forms no part of the present invention. Figure 2 is otherwise similar to Figure 1 and like parts have been indicated by like reference numerals. In Figure 2,. springs H2 and H4 act against the diaphragm 85 whereby the member He, carried by the dia phragm, is urged to the right or left, by the. springs depending on their relative adjustment. by the screws i6 and I I8. Accordingly, the pressure difference across. the diaph agm M may be: varied; by adjusting thescrews H6. and l8 In. Figure 2, if the springs H2 and H4 are adjusted; to. bias. the ember H1 in. one ection or its other, the valve H51 will not maintain equal pres; sures within the chambers 83 and 9t, but it will. mai tain, a. pr et rm n d r lati n. b twe n hese p es ures as d term ned by the. a us men Qt the springs As used in the specification and in the app nded claims Vent r e is a tube 198. at both ends with a minimum internal-diameter throat portion intermediate the ends of the tube, said tube being disposed for continuous flow therethrough of at least a portion of the fluid whose flow is to be measured.

While we have described our invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after under standing our invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. We aim in the appended claims to cover all such media fications.

We claim as our invention:

1. In a fiow measuring system: a duct through which a fluid is arranged to flow; first and second spaced Venturi tubes disposed within said duct; a housing; a movable member dividing said housing into first and second chambers; means providing a first passageway having one end opening into the throat of said first Venturi tube and having its other end communicatin with said first chamber; means providinga second passage,- way having one end opening into the throat of said second Venturi tube and having its, other end. communicating with said second chamber; means providing a third passageway communicating with both oisaid chambers; said member being movable in response to changes in the pressure in one of said chambers, relative to the pressure in the other of said chambers, for con trolling flow of said fluid through said first and second passageways and their respective charmv bers from said third passageway.

2. In a fiow measuring system. a duct through which a fluid is arranged to flow; first and second spaced Venturi tubes disposed Within said duct; means providing first, second, and third passa s Ways; said first passageway having one end opening into the. throat of said first Venturi tubeanfi said second passageway having one end opening into the throat of said second Venturi tube, said third passageway communicating with the other ends of said first and second passageways; and means arranged to automatically control flow of said fluid through said first and second passageways for regulating the pressure in said third passageway relative to the throat pressures of said two Venturi tubes.

3. In a ficw measuring system: a duct through which a fluid is arranged to flow; first and second laterally spaced Venturi tubes disposed within said duct; a housing; a movable member dividing said housing into first and second chambers; means providing a first passageway having one end opening into the throat of said first Venturi tube and having its other end communicating with said first chamber; means providing a second passageway having one end opening into the throat of said second Venturi tube and having its other end communicating with said second chamber; means providing a third passageway communicating at one end with both of said chambers and at its other end with said duct; and means movable by said member in response to an increase in thepressure in one of said chambers, relative to the pressure in the other of said chambers. for decreasing the flow of said fluid from said third passageway through said other chamber and that one of said first and second passageways communicating with said other chamber.

4. In a flow measuring system: a duct through which a fluid is arranged to flow; first and second laterally spaced Venturi tubes disposed within said duct; a housing; a movable member dividing said housing into first and second chambers;

means providing a first passageway having one end opening into the throat of said first Venturi tube and having its other end communicating with said first chamber; means providing a second passageway having one end opening into the throat of said second Venturi tube and having its other end communicating with said second chamber; means providing a third passageway in restricted communication with both said chambers; and means movable by said member in 1 within said duct; a housing; a member dividing said housing into first and second chambers; means providing a first passageway having one end opening into the throat of said first Venturi tube and having its other end communicating with said first chamber; means providing a second passageway having one end opening into the throat of said second Venturi tube and having its other end communicating with said second chamber; means providing a third passageway communicating with one of said chambers through a first restricted opening and communicating with the other of said chambers through a second restricted opening; and means movable by said member in response to an increase in the pressure in one of said chambers, relative to the pressure in the other of said chambers, for increasing the resistance to flow of said fluid from said other chamber to that one of said first and second passageways communicating with said other chamber.

6. The combination recited in claim 5 in which said third passageway is in restricted communication with said duct for fluid flow from said duct into said chambers.

7. In a flow-measuring system: a duct through which a fluid is arranged to flow; first and second laterally spaced Venturi tubes disposed within said duct; a housing; a member dividing said housing into first and second chambers; means providing a first passageway having one end opening into the throat of said first Venturi tube and having its other end communicating with said first chamber; means providing a second passageway having one end opening into the throat of said second Venturi tube and having its other end communicating with said second chamber; means providing communication between said duct and said chambers; said last-mentioned means including a third chamber in communication with said duct and a fourth chamber in restricted communication with said third chamber and communicating with said first and second chambers through first and second restricted openings respectively; and means movable by said member in response to an increase in the pressure in one of said first and second chambers relative to the pressure in the other of said first and second chambers, for increasing the resistance to flow of said fluid from said other chamber to that one of said first and second passageways communicating with said other chamber.

FRANCIS J. W'IEGAND. MARK R. ROWE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,087,929 Dodge Feb. 24, 1914 1,897,174 MacLean et al Feb. 14, 1933 1,948,044 Myers et al Feb. 20, 1934 2,024,059 Parker et a1 Dec. 10, 1935 FOREIGN PATENTS Number Country Date 240,870 Great Britain Oct. 5, 1925 433,549 Germany Sept. 2, 1926 

